The discovery that platinum complexes are active against tumors has brought about a renewed interest in metal complexes as a source for anti-cancer agents. Cisplatin, cis-[Pt(NH.sub.3).sub.2 Cl.sub.2 ], for example, has been singularly successful in bringing about a regression of testicular and ovarian tumors and, as a result, other platinum derivatives have been investigated for anti-tumor activity.
These developments have led to the exploitation of structure-activity relationships including the synthesis of palladium analogs. Most of these efforts have been directed to the preparation of neutral palladium compounds. However, many of these have failed to show any discernible activity and, as a rule, have low solubility in aqueous solutions. Moreover, structure-activity relationships which have been developed for platinum compounds would predict that only neutral compounds would have anti-tumor activity. (M. J. Cleare and J. D. Hoeschele; "Bioinorganic Chemistry", Vol. 2: page 187 (1973); and M. J. Cleare; "Coordination Chemistry Reviews", Vol. 12: page 349 (1974)).